1. Field of the Invention
The present invention relates to a heating roller of a hollow cylinder form, a heating device having the heating roller, a fixing device having the heating roller or the heating device, an image forming apparatus such as a copying machine, a facsimile machine, a printer, and a printing machine having the heating roller, the heating device or the fixing device, and a method of producing the heating roller.
2. Discussion of the Background
An image forming apparatus such as a copying machine, a facsimile machine, a printer and a printing machine generally includes a fixing device having a heating roller of a hollow cylinder form. The fixing device is a mechanism for fixing a toner image transferred onto a sheet.
The heating roller is made of metal in general, and is thinned for decreasing the heat capacity thereof so that heat response property thereof relative to a heating device which heats the heating roller can be improved. However, because of the thinning, the rigidity of the heating roller is decreased. When a heating roller 118 is used in a fixing device 116 illustrated in FIGS. 9, 10 and 11, a pressing roller 119 illustrated in FIGS. 9, 10 and 11 press-contacts the heating roller. Therefore, a bend is caused in the longitudinal direction of the heating roller 118 as illustrated in FIG. 9, or a crush is caused in the vertical direction of the shaft of the heating roller 118 as illustrated in FIG. 10. When the bend or the crush is caused in the heating roller 118, a gap is caused at a nip portion between the heating roller 118 and the pressing roller 119 as illustrated in FIG. 11, the bend or the crush becomes maximum in the center portion of the heating roller in the longitudinal direction thereof, and a nip width in a sheet-passing direction of the center portion becomes narrow. When the nip width thereof becomes narrow, a heat amount which is supplied to a transfer member, to which a toner image is transferred and which passes between the heating roller 118 and the pressing roller 119, becomes small, and a fixing failure occurs.
Such a failure becomes remarkable when the outside diameter of the heating roller 118 in the center portion in the longitudinal direction thereof is made smaller than that in both end portions in the longitudinal direction thereof in order to prevent wrinkles of the transfer member when the transfer member passes the nip portion. The failure becomes especially remarkable when the thickness of the heat roller 118 in the center portion thereof is made smaller than that in both end portions by cutting the outer circumference surface of the center portion.
In Japanese Laid-Open Patent Publication 10-228201, a technique has been proposed to perform material processing-hardening by adding an external force to the inner circumference surface and the outer circumference surface of a heating roller so that the strength of a heating roller is improved by the processing-hardening during material deformation. Further, in Japanese Laid-Open Patent Publication 10-039665, a technique has been proposed such that the strength of a heating roller is improved by forming a rib in the inner circumference surface of the heating roller.
However, an apparatus using the technique proposed in Japanese Laid-Open Patent Publication 10-228201 is large and has low productivity. Moreover, in the technique in Japanese Laid-Open Patent Publication 10-039665, the heat capacity of a heating roller is increased in the portion thereof in which the rib is formed, and thereby it is difficult to maintain a uniform temperature of the heating roller as the temperature is rising.
Preferred embodiments of the present invention provide a heating roller in which a bend or a crush is not caused to suppress the increase of heat capacity, even when a thin heating roller is used, and manufacturing can be relatively easily performed. The preferred embodiments of the present invention provide a heating device having the heating roller, a fixing device having the heating roller and a heating device, and an image forming apparatus such as a copying machine, a facsimile machine, a printer and a printing machine, etc. having the heating roller, the heating device or the fixing device, and a method of producing the heating roller.
According to a preferred embodiment of the present invention, a heating roller includes a core of hollow cylinder form, wherein a thickness of the core is greater in a center portion thereof than in both end portions thereof.
Further, in the heating roller, an inside diameter of the core is smaller in the center portion thereof than in the end portions thereof.
Further, in the heating roller, an outside diameter of the core is substantially constant in a shaft direction of the core.
Further, in the heating roller, an outside diameter of the core is smaller in the center portion thereof than in the end portions thereof.
Further, in the heating roller, the thickness of the core continuously increases from the end portions thereof toward the center portion thereof.
Further, in the heating roller, a difference of the thickness of the core between the end portions and the center portion thereof is set such that a nip width of the center portion thereof is substantially the same as that of the end portions thereof, and such that a difference of a temperature in a longitudinal direction of the heating roller, when the temperature is rising, is within a predetermined range.
According to another preferred embodiment of the present invention, a method of producing a heating roller includes drawing a core of hollow cylinder form, and cutting an outer circumference surface of the core, wherein a thickness of the core is greater in a center portion thereof than in both end portions thereof.
Further, in the method of producing a heating roller, during drawing, the core is drawn is such that an inside diameter of the core is smaller in the center portion thereof than in the end portions thereof.
Further, in the method of producing a heating roller, during cutting, the core is cut such that an outside diameter of the core is substantially constant in a shaft direction of the core.
Further, in the method of producing a heating roller, during cutting, the core is cut such that an outside diameter of the core is smaller in the center portion thereof than in the end portions thereof.
According to another preferred embodiment of the present invention, a heating device including a heating roller includes a core of hollow cylinder form, and a thickness of the core is greater in a center portion thereof than in both end portions thereof, and a heating element is configured to heat the heating roller.
Further, in the heating device, an inside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the heating device, an outside diameter of the core of the heating roller is substantially constant in a shaft direction of the core.
Further, in the heating device, an outside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the heating device, the thickness of the core of the heating roller continuously increases from both end portions thereof toward the center portion thereof.
Further, in the heating device, a difference of the thickness of the core of the heating roller between both end portions and the center portion thereof is set such that a nip width of the center portion thereof is substantially the same as that of the end portions thereof, and such that a difference of a temperature in a longitudinal direction of the heating roller, when the temperature is rising, is within a predetermined range.
According to another preferred embodiment of the present invention, a fixing device including a heating roller includes a core of hollow cylinder form, a thickness of the core is greater in a center portion thereof than in both end portions thereof, and a pressing roller is configured to contact-press the heating roller.
Further, in the fixing device, an inside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the fixing device, an outside diameter of the core of the heating roller is substantially constant in a shaft direction of the core.
Further, in the fixing device, an outside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the fixing device, the thickness of the core of the heating roller continuously increases from both end portions thereof toward the center portion thereof.
Further, in the fixing device, a difference of the thickness of the core of the heating roller between the end portions and the center portion thereof is set such that a nip width of the center portion thereof is substantially the same as that of the end portions thereof, and such that a difference of a temperature in a longitudinal direction of the heating roller, when the temperature is rising, is within a predetermined range.
According to another preferred embodiment of the present invention, the fixing device includes a heating device including a heating roller including a core of hollow cylinder form, wherein a thickness of the core is greater in a center portion thereof than in both end portions thereof, and a heating element configured to heat the heating roller. A pressing roller is configured to contact-press the heating roller.
Further, in the heating device, an inside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the heating device, an outside diameter of the core of the heating roller is substantially constant in a shaft direction of the core.
Further, in the heating device, an outside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the heating device, the thickness of the core of the heating roller continuously increases from both end portions thereof toward the center portion thereof.
Further, in the heating device, a difference of the thickness of the core of the heating roller between the end portions and the center portion thereof is set such that a nip width of the center portion thereof is substantially the same as that of the end portions thereof, and such that a difference of a temperature in a longitudinal direction of the heating roller, when the temperature is rising, is within a predetermined range.
According to another preferred embodiment of the present invention, an image forming apparatus includes a photoconductive member, a charger configured to charge the photoconductive member, an exposure device configured to form an electrostatic image on the photoconductive member, a developing device configured to develop the electrostatic image on the photoconductive member, a transfer device configured to transfer the developed image onto a sheet-like medium, and a fixing device configured to fix the transferred image onto the sheet-like medium, the fixing device including a heating roller including a core of hollow cylinder form, a thickness of the core being greater in a center portion thereof than in end portions thereof, a heating element configured to heat the heating roller, and a pressing roller configured to contact-press the heating roller.
Further, in the image forming apparatus, an inside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the image forming apparatus, an outside diameter of the core of the heating roller is substantially constant in a shaft direction of the core.
Further, in the image forming apparatus, an outside diameter of the core of the heating roller is smaller in the center portion thereof than in the end portions thereof.
Further, in the image forming apparatus, the thickness of the core of the heating roller continuously increases from the end portions thereof toward the center portion thereof.
Further, in the image forming apparatus, a difference of the thickness of the core of the heating roller between the end portions and the center portion thereof is set such that a nip width of the center portion thereof is substantially the same as that of the end portions thereof, and such that a difference of a temperature in a longitudinal direction of the heating roller, when the temperature is rising, is within a predetermined range.